Structure and process for the formation of TSVs

ABSTRACT

An integrated circuit structure includes a semiconductor substrate; an interconnect structure over the semiconductor substrate, wherein the interconnect structure comprises a top inter-metal dielectric (IMD); an opening penetrating the interconnect structure into the semiconductor substrate; a conductor in the opening; and an isolation layer having a vertical portion and a horizontal portion physically connected to each other. The vertical portion is on sidewalls of the opening. The horizontal portion is directly over the interconnect structure. The integrated circuit structure is free from passivation layers vertically between the top IMD and the horizontal portion of the isolation layer.

This application claims the benefit of U.S. Provisional PatentApplication Ser. No. 61/016,220, filed Dec. 21, 2007, and entitled“Through-Silicon Via,” which application is hereby incorporated hereinby reference.

TECHNICAL FIELD

This invention relates generally to integrated circuits, and moreparticularly to structures and manufacturing methods of through-siliconvias.

BACKGROUND

Since the invention of integrated circuits, the semiconductor industryhas experienced continuous rapid growth due to constant improvements inthe integration density of various electronic components (i.e.,transistors, diodes, resistors, capacitors, etc.). For the most part,this improvement in integration density has come from repeatedreductions in the minimum feature size, allowing more components to beintegrated into a given chip area.

These integration improvements are essentially two-dimensional (2D) innature, in that the volume occupied by the integrated components isessentially on the surface of the semiconductor wafer. Although dramaticimprovements in lithography have resulted in considerable improvementsin 2D integrated circuit formation, there are physical limitations tothe density that can be achieved in two dimensions. One of theselimitations is the minimum size needed to make these components. Also,when more devices are put into one chip, more complex designs arerequired.

An additional limitation comes from the significant increase in thenumber and length of interconnections between devices as the number ofdevices increases. When the number and length of interconnectionsincrease, both circuit RC delay and power consumption increase.

Among the efforts for resolving the above-discussed limitations,three-dimensional integrated circuit (3DIC) and stacked dies arecommonly used. Through-silicon vias (TSVs) are often used in 3DICs andstacked dies for connecting dies. In this case, TSVs are used to connectthe integrated circuits on a die to the backside of the die. Inaddition, TSVs are also used to provide a short grounding path toconnect the ground in the integrated circuits to the backside of thedie, which is typically covered by a grounded aluminum film.

FIG. 1 illustrates a conventional integrated circuit structure, whichincludes semiconductor chip 100 and TSV 112 formed therein.Semiconductor chip 100 includes substrate 110, on which integratedcircuits (not shown) are formed. Interconnect structure 116 is formedover substrate 110, and includes a plurality of metallization layershaving metal lines and vias (not shown) formed in dielectric layers(commonly referred to as inter-metal dielectrics). Passivation layer 118(often referred to as passivation-1) is formed on a top metallizationlayer. Aluminum pad 122 is formed on passivation layer 118 and isconnected to the metal lines in interconnect structure 116. Passivationlayer 120 (often referred to as passivation-2) is formed on passivationlayer 118. An opening is formed in passivation layer 120 to exposealuminum pad 122. TSV 112 is electrically connected to aluminum pad 122through copper line 124. Isolation layer 126 is formed to isolate TSV112 from substrate 110, wherein isolation layer 126 extends over the topsurface of passivation layer 120. Through this structure, TSV 112 iselectrically connected to the integrated circuits in semiconductor chip100.

The structure shown in FIG. 1 suffers from drawbacks. The formation ofpassivation layers 118 and 120 are inherited from legacy processes. Thestacking of passivation layer 118, 120, and insulation layer 126 notonly involves more complicated manufacturing processes, but theresistance of aluminum pad 122 and the contact resistance betweenaluminum pad 122 and its adjoining metal features further causes theincrease in RC delay. In addition, the material difference at theinterface between aluminum pad 122 and overlying copper line 124 maycause delamination. Accordingly, new TSV formation processes are neededto form more reliable TSV structures without increasing themanufacturing cost.

SUMMARY OF THE INVENTION

In accordance with one aspect of the present invention, an integratedcircuit structure includes a semiconductor substrate; an interconnectstructure over the semiconductor substrate, wherein the interconnectstructure comprises a top inter-metal dielectric (IMD); an openingpenetrating the interconnect structure into the semiconductor substrate;a conductor in the opening; and an isolation layer having a verticalportion and a horizontal portion physically connected to each other. Thevertical portion is on sidewalls of the opening. The horizontal portionis directly over the interconnect structure. The integrated circuitstructure is free from passivation layers vertically between the top IMDand the horizontal portion of the isolation layer.

In accordance with another aspect of the present invention, anintegrated circuit structure includes a semiconductor substrate; aninterconnect structure over the semiconductor substrate, wherein theinterconnect structure includes a top IMD; a top metal pad in the topIMD and having a top surface substantially leveled with a top surface ofthe top IMD; an opening extending into the interconnect structure andthe semiconductor substrate; a TSV in the opening; and an isolationlayer having a vertical portion and a horizontal portion physicallyconnected to each other. The vertical portion is on sidewalls of theopening. The horizontal portion extends over the top IMD and includes anopening exposing the top metal pad. The integrated circuit structurefurther includes a continuous metal feature including a vertical portionextending into the opening to form the conductor, and a horizontalportion connecting the conductor and the top metal pad.

In accordance with yet another aspect of the present invention, anintegrated circuit structure includes a semiconductor substrate; aninterconnect structure over the semiconductor substrate, wherein theinterconnect structure includes a top IMD; a top metal pad over the topIMD; an opening extending into the interconnect structure and thesemiconductor substrate; a conductor in the opening; and an isolationlayer having a vertical portion and a horizontal portion physicallyconnected to each other. The top metal pad has at least a lower portionin the horizontal portion of the isolation layer. The horizontal portionextends on sidewalls and edge portions of the top metal pad. Theintegrated circuit structure further includes a continuous metal featureincluding a vertical portion extending into the opening to form theconductor, and a horizontal portion connecting the conductor and the topmetal pad.

In accordance with yet another aspect of the present invention, a methodof forming an integrated circuit structure includes providing a wafer.The wafer includes a semiconductor substrate; and an interconnectstructure over the semiconductor substrate. The interconnect structureincludes a top IMD. The method further includes forming an openingextending into the interconnect structure and the semiconductorsubstrate; forming an isolation layer having a vertical portion and ahorizontal portion physically connected to each other, wherein thevertical portion is on sidewalls of the opening, and wherein nopassivation layer is formed vertically between the top IMD and thehorizontal portion of the isolation layer; filling the opening to form aconductor; and continuing the step of forming the conductor to form ahorizontal metal line over the conductor.

In accordance with yet another aspect of the present invention, a methodof forming an integrated circuit structure includes providing a wafer.The wafer includes a semiconductor substrate; an interconnect structureover the semiconductor substrate, wherein the interconnect structurecomprises a top IMD; and a top metal pad in the top IMD, wherein a topsurface of the top metal pad is substantially leveled to a top surfaceof the top IMD. The method further includes forming an opening extendingfrom a top surface of the interconnect structure into the interconnectstructure and the semiconductor substrate; blanket forming an isolationlayer over the top IMD and extending into the opening; forming anopening in the isolation layer to expose the top metal pad; filling theopening to form a conductor; and continuing the step of forming theconductor to form a horizontal metal line over the conductor, whereinthe horizontal metal line extends into the opening in the isolationlayer.

In accordance with yet another aspect of the present invention, a methodof forming an integrated circuit structure includes providing a wafer.The wafer includes a semiconductor substrate; and an interconnectstructure over the semiconductor substrate, wherein the interconnectstructure includes a top IMD. The method further includes forming a topmetal pad over the top IMD; forming an opening extending from a topsurface of the interconnect structure into the interconnect structureand the semiconductor substrate; blanket forming an isolation layer overthe top IMD and extending into the opening, wherein the isolation layerextends on sidewalls and portions of a top surface of the top metal pad;forming an opening in the isolation layer to expose at least a portionof the top surface of the top metal pad; filling the opening to form aconductor; and continuing the step of forming the conductor to form ahorizontal metal line over the conductor, wherein the horizontal metalline extends into the opening in the isolation layer.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention, and theadvantages thereof, reference is now made to the following descriptionstaken in conjunction with the accompanying drawings, in which:

FIG. 1 illustrates a conventional backend structure, wherein athrough-silicon via (TSV) is connected to an aluminum pad in apassivation layer;

FIGS. 2 through 10 are cross-sectional views of intermediate stages inthe manufacturing of embodiments of the present invention; and

FIG. 11 illustrates a first die stacked on a second die, wherein a TSVis used to interconnect the first and the second dies.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The making and using of the presently preferred embodiments arediscussed in detail below. It should be appreciated, however, that thepresent invention provides many applicable inventive concepts that canbe embodied in a wide variety of specific contexts. The specificembodiments discussed are merely illustrative of specific ways to makeand use the invention, and do not limit the scope of the invention.

A novel integrated circuit structure including through-silicon vias(TSVs, also referred to as through-wafer vias, or TWVs) and the methodof forming the same are provided. The intermediate stages ofmanufacturing an embodiment of the present invention are illustrated.The variations of the embodiment are then discussed. Throughout thevarious views and illustrative embodiments of the present invention,like reference numbers are used to designate like elements.

Referring to FIG. 2, wafer 2, which includes substrate 10, is provided.Substrate 10 is preferably a semiconductor substrate, such as a bulksilicon substrate, although it may include other semiconductor materialssuch as group III, group IV, and/or group V elements. Semiconductordevices, such as transistors (not shown), may be formed at the topsurface of substrate 10. Interconnect structure 12, which include metallines 18 and vias 16 formed therein, is formed over substrate 10 andconnected to the semiconductor devices. Metal lines 18 and vias 16 maybe formed of copper or copper alloys, and may be formed using thewell-known damascene processes. Interconnect structure 12 may includecommonly known inter-layer dielectric (ILD) and inter-metal dielectrics(IMDs). The IMDs include top IMD 14, which is the topmost layer of theIMDs. In an embodiment, top IMD 14 and the underlying IMD layers areformed of a same material. In other embodiments, top IMD 14 and theunderlying IMD layers may be formed of either the same or differentlow-k dielectric materials, such as carbon-containing low-k dielectricmaterials (for example, with dielectric constants less than 3.9, andmore preferably less than about 2.5), black Diamond™ (a trademark ofApplied Materials), un-doped silicate glass (USG), fluorinated silicateglass (FSG), oxides, and the like. Top IMD 14 does not function as apassivation layer, and preferably does not contain common passivationmaterials, such as silicon nitride, and the like.

Top metal pad 24 is formed on top IMD 14. Top metal pad 24 may beconnected to the semiconductor devices (not shown) at the top surface ofsubstrate 10 through vias 16 and metal lines 18. The materials of topmetal pad 24 may include metals selected from aluminum, tungsten,silver, copper, and combinations thereof. In an embodiment in which topmetal pad 24 is formed of aluminum or aluminum alloys, the formation oftop metal pad 24 includes blanket forming an aluminum layer, andpatterning the aluminum layer to form top metal pad 24. Alternatively,no further top metal pad 24 is formed on top IMD 14, and the metal pad18 ₁ in top IMD 14 acts as the top metal pad 24, as is also shown inFIG. 9B.

FIG. 3 illustrates the formation and patterning of photo resist 32. Afirst etch is then performed to form opening 34 in interconnectstructure 12. Substrate 10 is then etched to extend opening 34 intosubstrate 10, for example, using a dry etch. After the formation ofopening 34, photo resist 32 is removed.

FIGS. 4 and 5 illustrate the formation of isolation layer 38. Referringto FIG. 4, isolation layer 38 is blanket formed. Isolation layer 38 maybe formed of commonly used dielectric materials such as silicon nitride,silicon oxide (for example, tetra-ethyl-ortho-silicate (TEOS) oxide),and the like. In an exemplary embodiment, isolation layer 38 includessilicon nitride layer 38 ₂ on silicon oxide layer 38 ₁. In anembodiment, thickness T1 of isolation layer 38 is less than thickness T2of top metal pad 24. In other embodiments, the thickness T1 of isolationlayer 38 may be substantially equal to, or greater than, thickness T2 oftop metal pad 24. An exemplary thickness T1 of isolation layer 38 isbetween about 0.6 μm and about 1.5 μm.

Referring to FIG. 5, photo resist 40 is applied, which may be a layer ofspray coating. Photo resist 40 is then patterned, with the portiondirectly over top metal pad 24 being removed. The exposed portion ofisolation layer 38 is then etched, exposing the underlying top metal pad24. Photo resist 40 is then removed. In an embodiment, the opening overtop metal pad 24 is smaller than top metal pad 24, and hence isolationlayer 38 has remaining portions over the edge portions of the top metalpad 24.

Referring to FIG. 6, diffusion barrier layer 42, also sometimes referredto as a glue layer, is blanket formed, covering the sidewalls and thebottom of opening 34. Diffusion barrier layer 42 may include titanium,titanium nitride, tantalum, tantalum nitride, or combinations thereof,and can be formed using physical vapor deposition, sputtering, and thelike. Alternatively, diffusion barrier layer 42 has a compositestructure including barrier layer 42 ₂ on adhesion layer 42 ₁.

A thin seed layer 44, also referred to as an under-bump metallurgy(UBM), is blanket formed on diffusion barrier layer 42. The materials ofseed layer 44 include copper or copper alloys. However, other metals,such as silver, gold, aluminum, and combinations thereof, may also beincluded. In an embodiment, thin seed layer 44 is formed usingsputtering. In other embodiments, physical vapor deposition or electroplating may be used. Thin seed layer 44 may have a thickness of lessthan about 1 μm.

FIG. 7 illustrates the formation of mask 46. In the preferredembodiment, mask 46 is a dry film, and thus is referred to as dry film46 throughout the description, although it may be formed of othermaterials. Dry film 46 may be formed of an organic material such asAjinimoto buildup film (ABF). However, other materials such as Prepregor resin-coated copper (RCC) can also be used. When dry film 46 isformed of ABF, the ABF film is first laminated on the structure shown inFIG. 7. Heat and pressure are then applied to the laminated film tosoften it so that a flat top surface is formed. Thickness T3 of dry film46 is preferably greater than about 5 μm, and more preferably betweenabout 10 μm and about 100 μm. One skilled in the art will realize thatthe dimensions recited throughout the description are merely examples,and will be scaled with the down-scaling of integrated circuits.

Dry film 46 is then patterned. In an exemplary embodiment, the resultingTSV 50 (see FIG. 8) needs to be connected to the integrated circuits onthe top surface of substrate 10 through top metal pad 24. Accordingly,opening 48 is formed in dry film 46, exposing the portions of diffusionbarrier layer 42 and seed layer 44 over top metal pad 24, opening 34,and the region therebetween.

In FIG. 8, opening 34 is selectively filled with a metallic material,forming TSV 50 in opening 34. In the preferred embodiment, the fillingmaterial includes copper or copper alloys. However, other metals, suchas aluminum, silver, gold, and combinations thereof, may also be used.The formation methods preferably include electroless plating, althoughother commonly used deposition methods such as sputtering, printing,electro plating, and chemical vapor deposition (CVD) methods may also beused.

After opening 34 is filled, the same metallic material is continuouslyfilled into opening 48 (refer again to FIG. 8), forming metal line 52,also referred to as post-passivation interconnect (PPI) line 52, whichelectrically interconnects top metal pad 24 and TSV 50. Metal line 52has a thickness T4 of less than about 60 μm, for example, between about3 μm and about 50 μm.

In FIG. 9A, dry film 46 is removed, for example, by an alkalinesolution. As a result, the portions of UBM 44 underlying dry film 46 areexposed. The exposed portions of UBM 44 are then removed by a flashetching, followed by the removal of diffusion barrier layer 42. Theetchant used for etching diffusion barrier layer 42 does not attackmetal line 52. In an exemplary embodiment, the exposed portion ofdiffusion barrier layer 42 is removed using a fluorine-based etchinggas, and the etching is preferably anisotropic. In FIG. 9A andsubsequent figures, seed layer 44 is not being shown since it istypically formed of similar materials as TSV 50 and metal line 52, andthus it appears to be merged with TSV 50 and metal line 52.

FIG. 9B illustrates yet another embodiment of the present invention, inwhich no aluminum pad is formed over top IMD 14 to act as the top metalpad 24. Instead, metal line (or metal pad) 18 ₁ in top IMD 14 acts astop metal pad 24. In this case, isolation layer 38 is substantiallyflat. Again, no passivation layer(s) is vertically between top IMD 14and isolation layer 38. An opening is formed in isolation layer 38 toexpose top metal pad 24/metal pad 18 ₁, and metal line 52 extends intothe opening to contact top metal pad 24/metal pad 18 ₁.

In alternative embodiments, instead of forming TSV 50 and metal line 52using dry film, a damascene process may be used. The initial steps ofthis embodiment are essentially the same as shown in FIGS. 2 through 6.Referring to FIG. 7, instead of being a dry film, layer 46 may includecommonly used dielectric materials such as silicon oxide, polyimide,black diamond, or the like. Layer 46 is preferably formed of a materialdifferent from that of isolation layer 38. The thickness of layer 46 ispreferably equal to the desirable thickness of metal line 52 (as shownin FIG. 9A). Next, copper or copper alloy is filled into openings 34 and48, followed by a chemical mechanical polish (CMP) to remove excesscopper. The resulting structure is shown in FIG. 10. Optionally, layer46 may then be recessed to a level lower than the top surface of metalline 52, or removed completely.

Referring back to FIG. 9A, after the removal of the exposed portion ofUBM 44, portions of isolation layer 38 are exposed. The exposed portionsof isolation layer 38 may not be removed and may act as a passivationlayer. Alternatively, the exposed portions of isolation layer 38 may benitrided, forming silicon oxynitride or the like.

Metal line 52 as shown in FIGS. 9A and 9B may be used as a bond pad fordirect metal-to-metal bonding. In an embodiment, two dies are bondedface-to-face, and the metal line/pad 52 in one of the dies is bonded tothe metal line/pad 52 in the other die. In alternative embodiments, asshown in FIG. 11, metal lines 52 may be used for placing solder bumps66. For example, in a first die 62, protection layer 64 is formedcovering edge portions of metal lines 52, while center portions of metallines 52 are exposed through openings in protection layer 64 to formbond pads. Protection layer 64 may be formed of polyimide, for example.Solder bumps (or BGA balls) 66 are placed on bond pads 52. The bottomends of TSVs 50 may be connected to another die 70.

Advantageously, by using the embodiment of the present invention, theredundant passivation layers, and possibly aluminum pads, are no longerformed. This results in reduced manufacturing cost. In addition, whenthe aluminum pad is not formed, the resistance of the interconnectionstructure is significantly reduced. Experiment results have revealedthat by omitting the aluminum pad (refer to FIG. 9B), the resistance ofthe metal lines connecting TSV 50 and the semiconductor devices onsubstrate 10 may be reduced from about 1000 mΩ to about 100 mΩ.

Although the present invention and its advantages have been described indetail, it should be understood that various changes, substitutions andalterations can be made herein without departing from the spirit andscope of the invention as defined by the appended claims. Moreover, thescope of the present application is not intended to be limited to theparticular embodiments of the process, machine, manufacture, andcomposition of matter, means, methods and steps described in thespecification. As one of ordinary skill in the art will readilyappreciate from the disclosure of the present invention, processes,machines, manufacture, compositions of matter, means, methods, or steps,presently existing or later to be developed, that perform substantiallythe same function or achieve substantially the same result as thecorresponding embodiments described herein may be utilized according tothe present invention. Accordingly, the appended claims are intended toinclude within their scope such processes, machines, manufacture,compositions of matter, means, methods, or steps.

1. An integrated circuit structure comprising: a semiconductorsubstrate; an interconnect structure over the semiconductor substrate,wherein the interconnect structure comprises a top inter-metaldielectric (IMD); an opening penetrating the interconnect structure intothe semiconductor substrate; a conductor in the opening; and anisolation layer having a vertical portion and a horizontal portionphysically connected to each other, wherein the vertical portion is onsidewalls of the opening and the horizontal portion is directly over theinterconnect structure, and wherein the integrated circuit structure isfree from passivation layers in a space that extends in a verticaldirection between the top IMD and the horizontal portion of theisolation layer.
 2. The integrated circuit structure of claim 1 furthercomprising a top metal pad no lower than the top IMD, wherein the topmetal pad is connected to a metal line overlying the conductor, andwherein the metal line and the conductor comprise same materials andform a continuous region.
 3. The integrated circuit structure of claim2, wherein the top metal pad is over the top IMD, with no metal layervertically between the top IMD and the top metal pad.
 4. The integratedcircuit structure of claim 3, wherein the isolation layer extendsdirectly over edge portions of the top metal pad.
 5. The integratedcircuit structure of claim 2, wherein the top metal pad is in the topIMD, and wherein the metal line extends down to contact the top metalpad through an additional opening in the isolation layer.
 6. Theintegrated circuit structure of claim 5, wherein the top metal padcomprises copper.
 7. The integrated circuit structure of claim 1,wherein the integrated circuit structure is free from silicon nitridebetween the top IMD and the horizontal portion of the isolation layer.8. The integrated circuit structure of claim 1, wherein the isolationlayer comprises a layer selected from the group consisting essentiallyof an oxide layer, a nitride layer, and a composite layer comprising anitride sub-layer on an oxide sub-layer.
 9. The integrated circuitstructure of claim 1, wherein the top IMD comprises a material selectedfrom the group consisting essentially of un-doped silicate glass,fluorinated silicate glass, low-k dielectric material, black diamond,and combinations thereof.
 10. The integrated circuit structure of claim9, wherein the top IMD is a low-k dielectric layer.
 11. An integratedcircuit structure comprising: a semiconductor substrate; an interconnectstructure over the semiconductor substrate, wherein the interconnectstructure comprises a top inter-metal dielectric (IMD); a top metal padin the top IMD and having a top surface substantially level with a topsurface of the top IMD; an opening extending through the interconnectstructure and into the semiconductor substrate; a conductor in theopening; an isolation layer having a vertical portion and a horizontalportion physically connected to each other, wherein the vertical portionis on sidewalls of the opening, and wherein the horizontal portionextends over the top IMD and comprises an additional opening exposingthe top metal pad; and a continuous metal feature comprising a verticalportion extending into the opening to form the conductor, and ahorizontal portion connecting the conductor and the top metal pad. 12.The integrated circuit structure of claim 11, wherein the horizontalportion of the continuous metal feature extends down into the additionalopening in the isolation layer to physically contact the top metal pad.13. The integrated circuit structure of claim 11, wherein the isolationlayer comprises a silicon nitride layer on a silicon oxide layer. 14.The integrated circuit structure of claim 11, wherein the top IMD is alow-k dielectric layer.
 15. An integrated circuit structure comprising:a semiconductor substrate; an interconnect structure over thesemiconductor substrate, wherein the interconnect structure comprises atop inter-metal dielectric (IMD); a top metal pad over the top IMD; aconductor formed in an opening extending through the interconnectstructure and into the semiconductor substrate; an isolation layerhaving a vertical portion and a horizontal portion physically connectedto each other, wherein the top metal pad has at least a lower portion inthe horizontal portion of the isolation layer, and wherein thehorizontal portion extends on sidewalls and edge portions of the topmetal pad; and a continuous metal feature comprising a vertical portionextending into the opening to form a; through silicon via (TSV), and ahorizontal portion connecting the conductor and the top metal pad. 16.The integrated circuit structure of claim 15, wherein the top metal padcomprises aluminum.
 17. The integrated circuit structure of claim 15,wherein the horizontal portion of the continuous metal feature extendsdown into an additional opening in the isolation layer to physicallycontact the top metal pad.
 18. The integrated circuit structure of claim15, wherein the isolation layer comprises a silicon nitride layer on asilicon oxide layer.